This invention relates to an improvement of structure of a power transmission V-belt.
In a raw edge type rubber V-belt, according to this invention, a single or plural plies of plain weave fabric or twill weave fabric obtained by weaving crimped nylon yarns subjected to wooly treatment and cotton yarns, nylon yarns or polyester yarns are embedded in the lower portion of the compression section or bonded to the upper surface of the tension section. Alternatively, the fabric is provided for both the lower portion of the compression section and the upper surface of the tension section. The crimped nylon fiber high in stretchability extends in the longitudinal direction of the belt while the cotton yarns, nylon yarns or polyester yarns high in rigidity extend in the lateral direction of the belt. Short fibers are mixed in a compression rubber layer under the tensile member layer and in a tension rubber layer on the tensile member layer in such a manner that the short fibers extend in the lateral direction of the belt.
Hence, the flexibility in the longitudinal direction of the belt is increased to prevent the belt from being cracked. The rigidity in the lateral direction of the belt is increased to improve the side pressure durability thereof.
In general, the following conditions are required for a V-belt adapted to transmit power by the frictional force created between the belt and the pulley:
(1) The belt has a high flexibility and is rarely cracked, and (2) the belt is not deformed by the side pressure which is caused when the belt is in the pulley groove.
A variety of belts have been proposed to satisfy the above-described requirements for a V-belt. With respect to the condition (1), a V-belt in which a plain weave fabric obtained by weaving cotton yarns, i.e., warps and wefts in such a manner that the warps and wefts form a cross angle of 90 degrees is embedded in bias form has been proposed. A V-belt in which a fabric obtained by weaving cotton yarns, i.e., warps and wefts in such a manner that the warps and wefts form a wide cross angle of 120 degrees is embedded in bias form has been provided, in order to increase the flexibility of the belt. These V-belts have been put into practical use.
The first mentioned V-belt has an elongation at break of about 60%, and therefore is disadvantageous in that the stretchability in the bias direction is low. Accordingly, the belt has a tendency to crack. On the other hand, the latter V-belt has elongation at break of about 110%, and therefore the crack-resistance of the belt is improved to some extent. However, it is not always sufficient. That is, if the latter mentioned V-belt is bent reversely by a tension pulley, it may be cracked.
None of the two V-belt 90.degree. and 120.degree. in cross angle can meet the condition (2) described above. That is, since the warps and wefts of the fabric are oblique with respect to the lateral direction of the belt, the belt is deformed by the side pressure applied thereto when run. As a result, it may be dropped in the pulley (as much as about 1.0 mm). Thus, the two V-belts are not always satisfactory in performance.
In order to improve the side pressure durability, a V-belt has been proposed in which cords are inserted in the lateral direction of the belt. However, this V-belt is also disadvantageous in that, since the belt is bent by the pulley at all times, the upper and lower surfaces of the belt are liable to be cracked.